Decoding Finely Tuned Gamma Oscillations in Chronic Deep Brain Stimulation for Parkinson's Disease

BACKGROUND: Finely tuned Gamma (FTG) activity-spontaneous narrowband Gamma oscillations (sFTG) or entrained to half the stimulation frequency (eFTG)-is typically linked to on-medication states and dyskinesia in Parkinson's disease (PD), making it a potential physiomarker for adaptive deep brain stimulation (aDBS). However, its characteristics and determinants remain unclear. OBJECTIVES: This exploratory study examined FTG prevalence, clinical correlates, and associations with DBS parameters, to guide future prospective work. METHODS: Local field potentials recorded in the subthalamic nucleus (STN) of PD patients with Percept neurostimulator were retrospectively analyzed, based on a predefined set of clinically relevant questions. RESULTS: Among 67 patients (134 STNs), sFTG occurred in 19% of STNs, and 1:2 eFTG in 28%. FTG was always associated with a medication, stimulation, or a stun-effect induced ON-state or a combination thereof, but could occur independent of dyskinesia. sFTG was most often observed during the transition from β to eFTG (54%), and rarely co-occurred shortly with eFTG (19%). β activity often co-occurred with FTG (50%), showing an inverse power relation with 1:2 eFTG. The occurrence of 1:2 eFTG depended on stimulation amplitudes. In 12 STN (9%), subharmonic artifacts occurred. CONCLUSIONS: FTG seems to be associated with an overall ON-state, independent of dyskinesia. The ratio 1:2 eFTG likely reflects entrainment of the neural populations underlying sFTG, but can occur without prior occurrence of sFTG, depending on stimulation amplitude consistent with "Arnold's tongue" framework. Future research should further specify β and FTG subtype interactions, while accounting for artifacts. Combining these physiomarkers may improve aDBS algorithms. © 2026 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.